Note: Descriptions are shown in the official language in which they were submitted.
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MANUFACTURE OF METAL EXTRUSIONS
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This invention relates to the manufacture of
extrusions, more particularly metal extrusions.
Extrusion presses for metals, e.g. aluminium,
are commonly designed to operate on a regular cycle of
alternating extrusion periods and loading periods.
During the extrusion period, a ram operates within a
container to force a heated metal billet through an
extrusion die generally having up to six extrusion
apertures, and as extrusion proceeds the extruded
sections travel along a wide transfer table. During
the subsequent loading period, these extruded sections
are moved across the transfer table to a stretching
mechanism which stretches the section, generally by
about 1%, while the ram is retracted, the remnant of
the billet is ejected from the container and another
billet loaded into the container for the next extru-
sion.
Economic factors require that extrusion presses
operate at a maximum throughput in terms of weight of
metal extruded per hour, and with this objective the
extrusion cycle is made as short as possible. The
loading period is reduced to a minimum, typically of
less than 30 seconds. The extrusion time is also
reduced to a minimum by raising the speed of advance of
the ram, but an upper limit on this speed is set by the
requirement that the extruded metal must not melt in or
around the die, for melting spoils the surface finish
of the extrudate. This limit on extrusion speed can,
3 however, be raised by artificially cooling the extru-
sion die e.g. with water or liquid nitrogen~ The
extrusion alloy chosen is often a compromise between
the need for increased extrusion speed (which implies a
high melting point material), and the need for an
extruded section having defined properties (which may
imply a lower melting point material).
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The cross-sectional area of the extruded sectlon
is ~enerally not the maximum capable of bein~ handled by
the press in question. When thls i3 the case, the weight
of metal extruded per hour can be increased by the u~e of
an extrusion die having more than one hole. Dies having
two to six holes are common. However, a multi-hole
`extrusion die is more difficult to cool than a single
hole die, with the result that part of the increased
throughput gained by using a multi-hole die is lost by
the need to operate at a slower extrusion speed. The
output of an extruder can otherwise be increased to a
substantial extent by increasing the speed of extrusion
but there is a practical limit imposed by the fact that
the loading period cannot easily be reduced and
consequently forms an increasing proportion of the
total extrusion cycle time.
After emerging from the extrusion die, the
extruded sections cool unevenly, as a result of which
they become distorted or twisted on the transfer table,
and one function of the stretching operation is to remove
these distortions. When the extrusion die contains
several holes, metal is seldom extruded through all the
holes at precisely the same rate, with the result that
the extruded sections vary in length. It is possible to
reduce this difference by die correction, but that
materially increases extrusion costs. Because of these
twists, distortions and variations in length oP the
extruded sections, the stretching operation is
currently labour intensive.
The Applicants have devised a solution to this
complex problem of maximising the output of an extruder
which involves simultaneously reducing the combined
manning requirements of the extrusion and stretching
processes.
According to the invention in one aspect there is
provided a method of manufacturing an extruded section
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comprising the steps of employing a puller to grip a
leading edge portion of the section belng extruded and
to pull the section away from the extrusion die as
extrusion proaeeds, cooling the extruded section
rapidly and uniformly as extrusion proceeds, stopping
movement of the puller when the puller is a
predetermined distance away from the dies and
simultaneously stopping extrusion employing gripping
means to grip the extrusion at a location adjacent the
die, and then increasing the distance between the
puller and the gripping means by a predetermined amount
to stretch the extruded length while it remains in
alignment with the die.
The invention also provides apparatus for the
manufacture of extrusions comprising an extruder having
an extrusion die, a puller adapted to grip the leading
end of an extruded section emerging from the die, and
to pull said leading end of the section away from the
die as extrusion of the section proceeds, means for
rapidly and uniformly cooling the extruded section as
extrusion proceeds, gripping means disposed adjacent
the die and in alignment with the die lengthwise of the
extruded section, which gripping means is operable to
grip the extruded section, means for cutting through
the section at a location between the gripping means
and the die, and means operable to move the puller and
gripping means further apart to stretch an extruded
section gripped by the puller and the gripping means.
Preferably, the extruded length is severed between
the gripping means and the die before stretching of the
extruded length is initiated. Preferably also, the
gripping means is fixed during the stretching
operation, the stretching movement being performed by
the puller.
The extruded metal is preferably aluminium, which
term is used to cover not only the pure metal but also
Al-r;ich alloys, particularly those of the 6000 series
~of Aluminium Assoclation register) which are
conventionally used for extrusion.
In order to ensure that the extruded section does
not become substantially distorted or twisted,
intensive and uniform cooling is generally required
immediately downstream of the extrusion die. Although
the nature of the intensive cooling is not critical, it
is found that forced air or sprayed water is often
inadequate. Preferred cooling means comprise high-
pressure jets of water directed from all sides at the
extruded section. It is convenient from all sides at
the extruded section. It is convenient to pass the
extruded section through a tunnel in which are mounted
nozzles to project the high-pressure jets.
When the extrusion die has two or more die
apertures, it may be di~ficult or impossible to cool ll
extruded sections sufficiently rapidly and uniformly,
and it is greatly preferred that an extrusion die
having only a single extrusion aperture is used. This
has other advantages. Thus the die itself can be
intensively cooled, increasing the possible extrusion
speed, and the single aperture does not require
correction to match other apertures, so reducing the
cost of the die. Other advantages are described
herein.
According to a preferred feature of the invention,
the movement of the puller towards and away from the
die is actuated through a cable loop to one run of
which the puller is connected, and the stretching
movement is also transmitted tot he puller through the
cable. In one advantageous construction, said cable loop
extends about first pulley means adjacent the die and
second pulley means remote from the die, said second
pulley means comprising two pulleys rotatable about
parallel axes on a beam which is itself pivotable about
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a third axis parallel to and disposed mLdway between
said parallel axes, and there are provided means for
applying a brake to at least one of said two pulleys
and means for swivelling the beam about said third axis
thereby to apply a stretching force to the puller
through the cable.
The invention will now be described in more detail
with reference by way of example to the accompanying
diagrammatic drawings in which:
Figure 1 is a general view of an apparatus
incorporating the invention,
Figure 2 is a perspective view of the clamping and
shearing means of the apparatus,
Figure 2A shows part of the clamping and shearing
means of Figure 2,
Figure 3 is a perspective view of the puller of
the apparatus, partly cut away to show the
construction, and
Figure 4 is a side view of the mechanism for
actuating stretching of the extrusion.
Referring first to Figure 1 of the drawings, the
apparatus comprises an extruder 10, a puller 11 which
is movable towards and away from the extruder along a
guide rail 11a, a clamping and shearing head 12
disposed adjacent the extrusion die of extruder 10, and
a stretch actuating mechanism 13. The extrusion die
has a single die aperture.
At the commencement of a cycle of operations, the
puller 11 is disposed adjacent the clamping and
shearing head 12 and is operated to grip the leading
end of the extruded section which protrudes through the
head 12 and to pull the section along a transfer table
14 as extrusion proceeds. The puller generally
operates at a constant tension, merely sufficient to
prevent the extruded section from buckling or warping,
typically of the order of 50 - 100 kg (0.5 - 1.0 kN).
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The extruded section emerging from the die is drawn by
the puller through a cooling device in the form of a
tunnel 8 ln which pressure jets of water are directed
on to the section to cool it rapidly and unif'ormly~
The tunnel extends to a point close to the die.
Referring to Figures 1 and 3, the puller 11
comprises a trolley 15 equipped with four rollers 16
engaging within twin channel-section guide rails 11a so
that the trolley rolls along the rails, and a pair of
gripping jaws 17, 18. The lower jaw 17 is fixed and
the upper jaw 18 is swivelled to open and close the
jaws by a pneumatic actuator 20 controlled by a
solenoid-operated air valve. The trolley carries an
air reservoir 21 which communicates with the air valve
and which is automatically replenished each time the
pulley returns to its station adjacent the extruder 10.
The puller is driven along the guide rail 11a by a
loop of steel cable 24 the two ends 25 of which are
anchored to the trolley. From one of its anchored ends
the cable extends towards the extruder, round a pulley
26 mounted on the frame of the apparatus adjacent the
head 13, then to the opposite end of the apparatus
where it extends round a series of pulleys, and back to
the trolley 15. Electrical signals to operate the
solenoid controlling the air valve 21 are transmitted
through the cable 24, and the cable pulleys are
appropriately insulated from the trolley and the main
frame 27 of the apparatus.
When the extruded section reaches the desired
length, the puller contacts a line switch (not shown)
which stops a reversible electric motor driving cable
pulleys 29, 30 forming part of the said series of
pulleys at the end of the apparatus remote from the
extruder, and which also stops supply of pressure fluid
to the ram of the extruder 10. The leading end of the
extruded section remains gripped by jaws 17, 18. At
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this stage the clampin~ an~ shearing head 12 shown
diagrammatically in Figure 2 comes into operation.
Referring now to Figure 2, the head 12 is
supported by a frame 32 mounted on the main frame 27 of
the apparatus. The frame 32 has two uprights 33
between which is disposed a rectangular sub-frame 34
the bottom cross-member 35 of which is mounted on
horizontal pivots 36 carried by the bottom member of
the frame 32. A pneumatic actuator 37 has its air
cylinder secured to a horizontal limb 38 on one of the
uprights 33 and has its actuating rod 39 pivotally
connected to one of the uprights 40 of the sub-frame 34
so that the sub-frame can be swung between a vertical
position and the position shown in Figure 2 in which it
is tilted towards the extruder. Referring now also to
Figure 2A, the cylinder of a hydraulic actuator 42 is
mounted in a slideway between the uprights 40 of the
sub-frame so as to swivel with the sub-frame but to be
capable of movement axially of itself. A heavy
compression spring 41 is disposed between the bottom of
the cylinder of the actuator 42 and the bottom cross-
member 35 of the sub-frame. The upper end of the rod
43 of actuator 42 carries a gripping jaw 44 which is
thus movable towards and away from a fixed jaw 45
mounted on the sub-frame. The two uprights 40 of the
sub-frame have parallel T-pieces 46 secured to them
which carry between them a pivot rod 47 extending
parallel to the pivot 36 of the sub-frame. A first arm
48 (see Figure 2A) is pivotally mounted on the rod 47
and has its other end pivotally connected to the
movable jaw member 44 and rod 43. A second arm 49
pivotally mounted by one end on the pivot rod 47 has
secured to its other end a shearing blade 50 which co-
operates with the rearward edge of the movable jaw 44
to perform a shearing action, and a link 52 extends
between a pivot pin 53 carried by a lug 54 on the
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second arm and a second pivot pin 55 carriec~ by a lug
56 connected to the bottom end of the hydraulia
actuator 42. In operation of the apparatus, the jaws
44, ll5 are open and the sub-frame 34 is dlsposed in its
upright position by the pneumatic actuator 37 during
the whole of the time during which extrusion is taking
place. When the puller 11 is stopped and extrusion
ceases, pressure fluid is supplied to the hydraulic
actuator 42, and since downward movement of the
cylinder is resisted by the spring 41 the rod 43 moves
the movable jaw 44 upward and clamps the extrusion
firmly against the fixed upper jaw 45. Continued
supply of pressure fluid to the cylinder then overcomes
the resistance of the spring 41 and the cylinder moves
downward pulling the arm 52 and shear blade 50 down to
cut through the extruded section, leaving the tail end
of the section firmly gripped in the jaws while next a
stretching operation is carried out on the extruded
length.
The stretching operation is carried out by the
puller, actuated by the mechanism 13 illustrated in
Figure 4 to which attention is now directed.
The mechanism is mounted on a base frame 60
secured to the main frame 27 of the apparatus. ~n
upright frame 61 is pivotally mounted by its lower end
at 62 on the base frame and on its side further from
the extruder has a platform 63 carrying the electric
motor 28 which serves to drive the cable loop 24 to
which the puller is secured. For this purpose a drive
belt 64 extends round a pulley 65 on the motor shaft
and round a second pulley 66 secured on one end of a
drive shaft mounted in plummer block bearings 68
secured to the upper end of the upright frame 61. Two
toothed pulleys (not shown) are secured on the other
end of the shaft 67 and toothed belts extending about
these pulleys respectively serve to drive two further
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toothed pulleys (not shown~ secured on shafts 68, 69
carrled in bearing blocks 70, 71 Otl a beam 72 which is
centrally pivotally mounted on the drive shaft 67. The
two shafts 68, 69 have respectively secured to them two
pulleys, about which the puller cable 24 extends, and
two discs 73, 74 each of which has co-operating with it
a disc brake 75. When the brakes 75 are not applied,
motor 28 drives the cable 24 through the toothed belts
and pulleys and the cable draws the puller along the
guide rail lla.
A hydraulic actuator 78 having its cylinder
pivotally mounted in trunnions 79 on the upright frame
61 has its actuating rod 80 pivotally connected to one
end of an arm 81 which is rigidly secured to the beam
72 so that the actuator 78 operates to swivel the beam
about the shaft 67. The shafts 68, 69 of the drive
pulleys are equidistantly spaced on opposite sides of
shaft 67 and the axes of the three shafts are in a
common plane so that swivelling of the beam does not
alter the length of the cable loop. When the movement
of the pulley away from the die is stopped by the limit
switch, the disc brakes 75 are automatically applied
and the hydraulic actuator 78 is extended, and the
bottom run of the cable 24 is thus drawn towards the
upright frame 61 and carries the puller with it which
in turn stretches the extruded section. The cable 24
moves as necessary about the pulley 26 adjacent the
extruder during this operation.
The extent of swivelling movement of the beam 72
and hence of stretching of the extrusion is adjustable
by means of a series of switches 85 spaced along an
arcuate strip 86 mounted on the upright frame 61. When
an element 87 connected to the free end of the arm
strikes the selected switch 85, the hydraulic supply
circuit of the actuator is disconnected from the lower
end of the actuator cylinder and connected to the upper
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end of the cylinder to return the beam 72 to it3
original position. The actuators of` the Jaws of the
puller and the clamping head 12 are then operated to
release the extruded section, which is transferred
laterally to a conveyor or a receiving table by means
not shown, and the motor 28 is reversed to drive the
cable in the opposite direction to return the puller
rapidly to its starting position adjacent the extruder.
At the same time the pneumatic actuator 337 is operated
to move the sub-frame 34 to the inclined position in
which it is shown in Figure 2, causing the end of the
extrusion to be exposed between the open jaws 44, 45
for gripping by the jaws of the puller. Extruding
movement by the ram is then resumed. As soon as the
puller has moved away from the head on the next cycle
of operations, the sub-frame 34 is returned to its
upright position.
In order to maintain a suitable tension in the
cable 24 a hydraulic actuator 90 is connected between a
part of the fixed frame 60 and the pivoted upright 61,
and a wedge 91 then falls under gravity into a gap
between one end of an open box part 92 connected to the
fixed base and an element tnot shown) connected to the
upright 61 and projecting vertically into the box. The
wedge thus operates automatically to take up any slack
in the cable so that the actuator 90 can be de-
activated until further tightening adjustment is
required.
The apparatus described above has numerous
advantages as follows:
(1) The fact that the single extrusion is held in the
puller during cooling and subsequent stretching
obviates the necessity to locate the end of the section
end as is required if one wishes to automate the
stretcher on a normal press.
(2) The elimination of a ~ide cooling transfer table
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reduces to a remarkable degree the building spaoe
required for the press layout.
(3) The fact that sections are cold upon all
subsequent handling from the press reduces
significantly the damage which occurs when hot sections
are moved on a normal press transfer table.
(4~ The fact that the time between when a section is
extruded and when it is sawn to length amounts to only
a few minutes (typically 5 minutes) when compared to a
normal press (typically 35 minutes) reduces the risk of
defective material being inadvertently produced in
large quantities.
(5) The use of dies with a single extrusion aperture
on a small container, as opposed to multiple-aperture
dies on a large container, enables much closer
dimensional tolerances to be achieved.
(6) The fact that a press with a small container and a
single-aperture due will extrude much faster (by die
cooling, container cooling, section cooling etc) than a
multiple-aperture press means that it can achieve the
same productivity as or a higher productivity than a
large press.
(7) The use of a single-aperture due and a small
container as described above provides the option of
coating the extrusion with a cladding of a different
composition metal to obtain enhanced surface
properties.
Thus one obtains full automation, reduced damage,
closer tolerances, and reduced losses through
accidentally produced sub-standard material. In
addition, and most importantly, the building space
occupied by two or even three small single aperture
presses is no greater than the building space occupied
by one normal multiple-aperture press. In addition, by
the elimination of costly transfer tables (typically 2"
container 500 m.ton capacity) for a normal multiple-
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aperture press (typically 7" container 2,000 m.ton
capacity) then the capital cost of the press and lts
ancillary equipment is considerably less; typically,
three presses with all ancillary equipment as described
and illustrated would cost the same as one normal
multiple-aperture press.
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